(1) Field of the Invention
The present invention relates to electrochemical electrodes, and more specifically to a method of fabricating a magnesium titanium bipolar electrode.
(2) Description of the Prior Art
There continues to be a need for energy sources with a high energy density. In particular, there is a need for high energy density energy sources that can power unmanned undersea vehicles (UUVs). Such energy sources when used to power such vehicles are required to have an energy density greater than 400 Wh kg−1. They also need to have long endurance and quiet operation. Additionally, they must be relatively inexpensive, environmentally friendly, safe to operate, reusable, capable of a long shelf life and not prone to spontaneous chemical or electrochemical discharge.
The zinc silver oxide (Zn/AgO) electrochemical couple has served as a benchmark energy source (at 100 Wh kg−1) for undersea applications. Because of its low energy density, however, it is not suitable for unmanned undersea vehicles whose energy density requirements are four times those of the Zn/AgO electrochemical couple.
In an effort to fabricate power sources for unmanned undersea vehicle with increased energy density (over zinc-based power sources), research has been directed towards semi fuel cells (as one of several high energy density power sources being considered). Semi fuel cells normally consist of a metal anode, such as magnesium (Mg) and a catholyte such as hydrogen peroxide (H2O2). To achieve high energy, a multi-cell stack of semi fuel cells is required. This necessitates the use of bipolar electrodes. The electro-active components of a bipolar electrode are a catalyst cathode of palladium iridium on a substrate for the fast electrochemical reduction of hydrogen peroxide, electrically connected to a metal anode such as magnesium. Both halves of the bipolar electrode should be as physically close together as possible, while at the same time isolating the catalyst cathode and metal anode for the other's electrolyte. In order to accomplish isolation of the cathode and anode from the other's electrolyte, the bipolar electrode requires a chemically inert, nonporous, electronically conductive barrier between the metal anode and the catalyst cathode. One suitable material for such a barrier would be titanium metal. A titanium barrier would need to be in electrical contact with the catalyst cathode and the magnesium anode. Unfortunately, titanium and magnesium react differently under extreme thermal conditions making it difficult to bond a titanium barrier to a magnesium anode in such a way as to maintain electrical contact between the two surfaces over high temperatures for long durations. What is needed is a method of fabricating a magnesium-titanium template for a bipolar electrode such that the titanium barrier and the magnesium anode maintain electrical contact between the two surfaces under all operating conditions.